Help!

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91lincTownEx

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Well I have been having my voltage drop for no reason lately. I've replaced my battery, alternator, bat. cable clamps, starter relay, and the spark plugs all replaced and still when I pull up to a light my lights exterior and interior lights dim. I put in a voltometer and normal operating volts its at 13 but will drop to like 9 or so. Sometimes when im at a light it I just barely hold the brake just enough to stay stopped my voltage will go back up but not always. When im in neutral or park the volts stay normal but when I go to reverse or drive they will drop. But all of this doesnt always happen sometimes it will run and act perfectly, but the next minute not. So I was thinking it could maybe be a loose connection or a short somewhere? I dont have any idea.
 
i notice you have a system in your car, does the voltage drop when you are pumping your system? or is it just when you are driving normally?
 
No, it does it anytime, it will do it when im at a light with my system on or off. But only some times. I can be setting at one light with my system all the way up, then at the next light ill have to have the system off and holding the brake while giving it a little gas. I think my alternator like turns off or something. Cause it will be fine when I first turn it on but after a while i hear this noise and then the voltage will start dropping. What gets me is it will only do it when im either in reverse and in drive. If im at a light and the voltage drops I can put it in neutral and it will go right back down.
 
Im thinking two possible things. Something to do with your brake system like a bad ground is shorting or causing resistance and that would drop battery voltage. Or the there is a wire that goes to the alternator that energizes the stationary field. (i believe thats right) either that or one of the stator fields. On the old towncar with the pigtails i believe its in the extra three pin plug and activates charging.
 
When I come up to a light im on my brake and at about 5 mph my voltage will just drop. I just checked all the grounds and connections up top that are easily accessable(sp) they are all fine. Where is the ground for the brake? Thanks for your help!
 
It is in the back somewhere with the tailight harness. I dont believe that the brake lights would draw enough resistance to slow down the alternator that bad. But grounds can be kinda screwy.

That sounds like its possibly the alternator. Alternators have a starting efficiency that requires a certain RPM and if the alternator has worn it can not be as efficient right at that 600 rpm idle. I would have that alternator tested.
 
Something to remember

Alternators really only start to produce excess voltage when the RPM level is above somewhere in the neighborhood of 1100 RPM. At idle and slightly above, the alternator will produce just enough voltage to keep the car with accessories running at a constant state. High draw devices will eventually cause the alternator to fail to the point where the fields will not produce enough current to keep the battery at peak charge. Did the issue go away after replacing the battery and alternator and then return after a while?? A high draw system needs to be connected to CAPS to keep the system constantly at the correct voltage level so as not to cause over heating and deterioration of the system. Make sure that your system is connected properlt with oversized cables, properly terminated, properly fused, and the ground wire is of sufficient size and connected to a good body ground. Also make sure that the ground straps from the engine to the frame are in good condition. Bad grounds are the most popular reason for electrical failures and the cause of the majority of vehicle electrical fires.
 
I have found a ground cable that hangs down from a ground point looks as though it has/was ripped or something. It is back by my right rear wheel. It connects to the bottom corner of the body, but I cant find out where it was connected to can anybody see where theres connects to? Thanks!
 
I think i had one attached to my exhaust pipe, lol. Im not sure if it was supposed to be there, but it was.
 
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